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Math Help - Find Cos

  1. #1
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    Find Cos

    ok so i guess i am a little foggy from the summer break. can someoen help me with this question?

    if cos t = (4/5), then find cos (t + pi)

    I am totally lost, so please help me.
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  2. #2
    Senior Member JaneBennet's Avatar
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    \cos(t+\pi)=\cos{t}\cos{\pi}-\sin{t}\sin{\pi}

    Take it from there.
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  3. #3
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by zooanimal98 View Post
    ok so i guess i am a little foggy from the summer break. can someoen help me with this question?

    if cos t = (4/5), then find cos (t + pi)

    I am totally lost, so please help me.
    Let's try to see what \cos (t + \pi) simplifies to, in terms of sine and cosine...

    \cos (t + \pi)=\cos t\cos\pi-\sin t\sin\pi <-- Sum Identity

    Note that \cos\pi=-1\text{ and }\sin\pi=0

    Thus, our expression simplifies to \cos(t+\pi)=-\cos t

    I'm sure you can take it from here...

    I hope this helps

    --Chris

    EDIT: JaneBennet beat me...
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  4. #4
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    is the answer -4/5?

    i guess i am a little on the slow side. does that mean the answer is -4/5?
    if not then well i guess i still need a better explantion

    Quote Originally Posted by Chris L T521 View Post
    Let's try to see what \cos (t + \pi) simplifies to, in terms of sine and cosine...

    \cos (t + \pi)=\cos t\cos\pi-\sin t\sin\pi <-- Sum Identity

    Note that \cos\pi=-1\text{ and }\sin\pi=0

    Thus, our expression simplifies to \cos(t+\pi)=-\cos t

    I'm sure you can take it from here...

    I hope this helps

    --Chris

    EDIT: JaneBennet beat me...
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  5. #5
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by zooanimal98 View Post
    i guess i am a little on the slow side. does that mean the answer is -4/5?
    if not then well i guess i still need a better explantion


    --Chris
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